[Shiny]

2018 Silverado 1500 5.3 and a ~4500 lb camper

No issue on paved roads when over ~30mph - the temp is rarely over about 185. But the transmission overheats when moving slow uphill. Pulling up a hill at slow speed, the fluid gets way too hot. We just went camping and the fluid hit 245 as we pulled into the campsite after creeping uphill for a couple miles. Elevation may not help but that's where we live (campground most recently was at 9800 ft).

Chevrolet does NOT offer an auxiliary cooler for my truck so I am looking for aftermarket options.

The only "direct fit" cooler I could find is made by Mishimoto. Seems a good brand. Will this solve my problem?

One mechanic I called about installation said I'd be better off adding a bigger pan to increase fluid capacity. I'm not sure I buy into the physics here, unless the pan helps dissipate heat. I can see more fluid taking longer to heat up but will this help dissipate it? Please educate me on the tradeoffs and options.

Given the issue is clearly aggravated by low airflow, should I look for a cooler with a fan?

Any and all advice is welcomed.

Thanks,

Mike

[SRR]

See if Derale makes a deeper pan with the cooling tubes for it or an aluminum pan with cooling fins, easy to install without mods.

[dataway]

My 2011 GMC with a 5.3 has a factory installed cooler, part of the tow package ... maybe you could scare up the OEM parts for one?
I towed a gooseneck trailer/camper right about that weight up and down lots of small mountains without an issue, using tow/haul mode on the steeper grades.

This particular truck has the tow package and HD cooling package, trans cooler, oil cooler, power steering cooler. I can try to get some pics of what's there.

[Shiny]

Thanks for the replies.

SRR - I'll look into the pan with enhanced cooling. I will ask dealer about it too, as I'm not sure if I have any warranty left but if so, don't want to risk losing coverage.

dataway - that's what I was expecting... better cooling if equipped with a towing pkg. My truck doesn't have it, so I expected Chevy would have a bolt-on cooler that would come with that package. They do not. Towing package on my truck would basically add an integrated brake controller and a little lower rear ratio, but no increased cooling capacity. Go figure.

I was disappointed to learn I couldn't even install the OEM integrated controller, as that would be nice to have. Just seems weird this truck could be equipped to tow a lot more than mine, yet the cooling system can't handle our trailer... Oh well, the engineers and warranty people have the "margins" down to a science for sure!

When I hear back from the dealer (they owe me a quote to install the Mishimoto cooler) I'll ask about using the prior generation cooler. Thanks for the info!

Mike

[Skip Fix]

Pretty sure my 2015 with the 6.2 gas motor and towing package has one also. I know my 97 with tow package does it sits in front of the radiator.

[Shiny]

Mishimoto web site (link) says the cooler in my truck is "integrated with the AC condensor".



This was apparently introduced for 2014 in the spirit of (forgive my sarcasm) "pay more, get less" or engineering "optimization" when cost is king.

Regardless, Chevy has no option for me.

Derale does make a deep pan with cooling tubes so I'll ask the dealer about that also.

[72projectbird]

Had a 2014 with a 5.3 that liked to get the trans nice and hot when towing. I dunno why GM struggled with cooling the transmissions on that generation truck?

I've added universal large coolers to almost every truck I've owned. Usually I'll run them using the stock cooler as basically a pre-cooler. Leave the trans line running into the inlet side of the factory cooler, run a return from the outlet of the factory cooler into the inlet of a huge aftermarket cooler, and run the factory return trans line to the outlet of the aftermarket cooler. Never had any heat issues. Sometimes I'll even run a small electric fan on top of the aftermarket cooler.

[Formulabruce]

/\/\ / \ Exactly what he said, I do same thing.. some of the trans coolers now have compact fans installed on them I notice

[chuckies76ta]

I had a 2004 that I installed one of these on. I removed the GM cooler. I wired it up with a switch on the dash and would turn it on manually when towing if the temp started to rise. It worked very well.. Just remember to try stay away from rubber hoses and hose clamps. Threaded fittings, or compression fittings and metal lines. Also, there are proper ways to mount the cooler.
https://www.holley.com/products/cool...rs/parts/70297

[Mr Anonymous]

The "integrated" coolers have a known leaking issue where the connection is made to the cooler. I'd take that out of the loop (pun intended) and add a large aftermarket cooler.

[buds56]

IMO the best thing you can do to get the temp down in the trans is to install a bypass kit in the trans thermostat.
Until the fluid temp reaches 192 deg. no fluid goes through the cooler.until this thermostat opens.

There is quite alot on the internet about this and the 6l80, I think it's worth researching.
Good Luck

[78w72]

Originally Posted by 72projectbird

Had a 2014 with a 5.3 that liked to get the trans nice and hot when towing. I dunno why GM struggled with cooling the transmissions on that generation truck?

I've added universal large coolers to almost every truck I've owned. Usually I'll run them using the stock cooler as basically a pre-cooler. Leave the trans line running into the inlet side of the factory cooler, run a return from the outlet of the factory cooler into the inlet of a huge aftermarket cooler, and run the factory return trans line to the outlet of the aftermarket cooler. Never had any heat issues. Sometimes I'll even run a small electric fan on top of the aftermarket cooler.

this is the best way to route a aux cooler for any street driven vehicle... not using the radiator trans cooler first will lose any low speed cooling since an aux cooler needs air flow to work, unless its a fan one, mount it in front of the radiator & a/c condenser near the grill opening.

also a good idea if towing to use a synthetic ATF, valvoline maxlife is the best value available at any aprts store or walmarts for about $20/gal & is an excellent fluid compatible with most makers but of course read the label first.

[Shiny]

Lots of good input, thanks all.

Still waiting on the dealer to respond, but leaning toward their recommendation to add the Mishimoto external cooler. It is the only brand that maintains the factory connections, which is appealing. It is also the only brand that has mounting brackets for this generation truck which I also find appealing.

As I understand, the truck does have a bypass valve. To me, this sounds like a thermostat that keeps fluid out of the cooler until it hits about 190. I have read some advice online to "bypass the bypass" and run the fluid through the integrated cooler all the time. I suspect there's a reason GM uses the valve, probably related to viscosity reduction, so I'm not jumping on this. It really won't address overheating when I'm towing since it doesn't increase cooling capacity.

As this is only a low-speed issue, it is logical that forced airflow is needed. The Mishimoto and many others are mounted between the fan and the radiator, which is rational. If I mounted a cooler somewhere else, I think it would need a fan, like the B&M or Derale units that have the fan integral.

After reading about the bypass valve, I will ask the dealer if it's possible for that to fail. When I'm not towing, the temperature is always below 190 so maybe it's not closing when it needs to?

As to fluid, I read the 6L80e uses synthetic fluid that is super stable to 240 so the risk is probably more about seals and internal friction surfaces than total fluid breakdown.

Thanks again. I'm always trying to learn and you on this forum are good teachers.

[Bills Auto Works]

In my opinion, the Mishimoto is the best aftermarket cooler for trucks!

I have installed them in both my LB7 Duramax/ Allison auto trucks, they BOTH have over 600,000 miles on them each with original engines & transmissions. Before adding the coolers, I put the BullyDog shift improver kits & 2 quart deeper cast aluminum pans on both as soon as I purchased the trucks.

Both these trucks are used almost exclusively to tow my trailers for transporting customers cars & never really had very much of a trans temp. problem...Once in a while on a really hard pull up a mountain out west with 100+ outside temps, the trans would get up to 210-215. I was completely shocked after putting the Mishimoto coolers on just how much lower the temps were! They advertise 20-30 degrees lower & mine are every bit that if not more. One thing I did have to watch was in the dead of winter the trans temp never even got to 100 degrees & the converter will not kick until 84 degrees trans temp. I fashioned a couple of pieces of plexiglass & covered a little more than a 3rd of the grill on those really cold trips which helped a bit!!!

Sure they are pricier than the cheapo ones but they work & a trans is a whole bunch more costly! I once saw on another forum some clown had 2 of the cheapo ones hooked together & was still driving around with his grill off because he couldn't tow without the trans temps getting high! Just like transporting, you get what you pay for!

God Bless
Bill
https://www.jalopyjournal.com/forum/...closed.614419/

[77 Canamman]

My 2017 GMC Sierra 1500 has the active grille shutters. Your 2018 should also have it. This ill conceived feature is supposed to save fuel, but I believe the disadvantages outweigh the advantages. My 6L80 6 speed trans usually runs 170-180 degrees F not towing, but freeway use 75-80 in the Summer. Wondering if the lack of airflow is the reason for the undesirable temps at freeways speeds under load.

[Shiny]

I'm unfamiliar with active grill shutters, something else to learn!

And mine also is typically 170 to 185 when I'm not towing... but 15 mph uphill towing, the fan and cooler are not getting it done.

[Bills Auto Works]

For comparison sake,,,, My trucks are running 140-160 pulling the loaded trailer on level ground with ambient temps 70-80 deg with the Mishimoto cooler.

God Bless
Bill
https://www.jalopyjournal.com/forum/...closed.614419/

[72projectbird]

I hate grill shutters. If you unplug them it'll throw a CEL, but if you get in there and disable the shutters from the motor that activates them, and leave the motor plugged in you shouldn't get a light on. It still thinks they're hooked up.

[Shiny]

Originally Posted by 72projectbird

I hate grill shutters. If you unplug them it'll throw a CEL, but if you get in there and disable the shutters from the motor that activates them, and leave the motor plugged in you shouldn't get a light on. It still thinks they're hooked up.

Originally Posted by 77 Canamman

My 2017 GMC Sierra 1500 has the active grille shutters. Your 2018 should also have it. This ill conceived feature is supposed to save fuel, but I believe the disadvantages outweigh the advantages. My 6L80 6 speed trans usually runs 170-180 degrees F not towing, but freeway use 75-80 in the Summer. Wondering if the lack of airflow is the reason for the undesirable temps at freeways speeds under load.

Thanks for info on the shutters. I looked and it appears my truck does have those. When I started it, they were open and never moved...

Assuming they are there to speed up the warming for emissions/efficiency, what is the problem with them?

[Shiny]

I learned the transmission cooler has a thermostat - they call it a bypass valve. It stays closed until fluid hits ~190 and then routes the fluid through the integrated cooler. Below 190, the fluid never goes through the cooler. As I experience and others in this thread have suggested, 190 doesn't happen during normal driving.

One dealer I talked to thinks mine is not working and recommends replacing it. He does not think they can diagnose to confirm first.

His logic: there are hundreds of my generation pulling trailers in his service area and they don't hear complaints like mine. He also said they stock the parts and agreed that means this is not a totally rare issue. I did not ask if he had related service bulletins.

The other dealer said he could install the Mishimoto cooler for ~2hrs labor.

I'm leaning toward doing both, as it will be less than a new transmission!